MSK Protocols

CT Protocols

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Fetal Radiation

Radiation doses to the fetus for selected procedures are tabulated below. The doses are expressed in millirads. Unlike nuclear medicine studies, radiographic studies are subject to wide variability in operator-dependent parameters. These parameters include skin entrance dose (which depends upon KVP and MAS settings), beam filtration, tube output (roentgens per minute), total fluoroscopic "beam on" time and the number and location of "spot" films taken. Because of the uncertainties in these parameters, these fetal dose values are considered to be approximations only. The parameter values used in calculating these doses are in part derived from U.S. national averages as compiled in NCRP Report 100, and in part from experience with actual Duke studies. Accordingly, these dose values should be used only as a guide to determining a subsequent course of action, and not as "hard and fast" numbers.

The fetal doses appear in colored cells. The colors reflect the degree of risk to the fetus associated with the study. Procedures with "green" cells generally carry zero to minimal risk of harm. Studies with "yellow" cells incur doses for which the risk is possibly increased, but for which little supporting data is available. Studies with "red" cells can incur doses within the range of those associated with teratogenicity, mental retardation and secondary childhood cancers. For these studies, a more accurate dose reconstruction should be obtained.

Assumes five minutes fluoroscopy time, 22 pelvic/abdominal spot films. Will be highly variable based on skill of operator.

Pitch for 5-mm Collimation CT

Estimated Fetal Dose (mGy)

1:1

17.5

1.4:1

12.5

2:1

8.7

CT Angiography of the Chest versus Ventilation-Perfusion Scanning

CT angiography has a higher sensitivity (81%–91%) and specificity (93%–97%) than ventilation-perfusion scanning for detection of emboli in the main, lobar, and segmental pulmonary arteries. The sensitivity of a high probability ventilation-perfusion scan is only 41%. Most recent articles state that the radiation dose to the fetus from CT angiography of the maternal chest is similar to or lower than that from a ventilation-perfusion scan.

Examination

Calculated Dose (mSv)

First Trimester CT Angiography

0.003-0.020

Second Trimester CT Angiography

0.007-0.076

Third Trimester CT Angiography

0.051-0.130

Lung Scanning

0.100-0.370

Contrast and the Fetus

Use of Intravenous Iodinated Contrast Material during Pregnancy

The fetus is exposed to iodinated contrast media because the contrast agent crosses the placenta. These constitute U.S. Food and Drug Administration category B drugs; that is, animal reproduction studies have not demonstrated a fetal risk, but there are no controlled studies in pregnant women, and they should be used only after assessing the potential risk-benefit ratio.

Depression of fetal thyroid function is a potential harmful effect that can be produced by exposure of the fetal thyroid to free iodide. However, the likelihood is that the fetal thyroid is exposed to the free iodide for only a short time. To our knowledge, there is a lack of well-controlled studies to assess these effects. If the mother received any iodinated contrast material during her pregnancy, the thyroid function of her baby should be checked in the first week of life, which is already standard practice in the United States for all newborns irrespective of prenatal iodide exposure.

Use of Intravenous Paramagnetic Contrast Agents for MR Imaging in Pregnancy

Animal studies show potential fetal toxic effects of intravenous gadolinium contrast agents. Growth retardation and congenital anomalies have been observed when these agents were administered at doses two to seven times higher than those used in humans. Gadopentetate dimeglumine has been used in pregnant women, inadvertently as well as for clinical purposes. To our knowledge, there have been no known adverse effects to human fetuses to date. The American College of Radiology’s 2007 white paper for safe MR practices addresses this issue. The paper emphasizes the need for a "well documented and thoughtful risk-benefit analysis" and that the decision to use contrast agents should be "based on overwhelming potential benefit to the patient and fetus outweighing the theoretic, but potentially real, risks of long-term exposure of the developing fetus to free gadolinium ions".

Use of Intravenous Contrast Agents during Lactation

The levels of iodinated and gadolinium contrast agents in the neonatal circulation from breast-feeding after the lactating mother has received any of these intravenous agents are reportedly very low. The risk from this low exposure is not sufficient to justify the cessation of breast-feeding for 24–48 hours. Thus, breastfeeding may be continued as usual after administration of intravenous contrast agents to a lactating mother.